The manufacture of modern semiconductor devices typically involves the deposition of viscous materials, such as polyamides, to substrates. Often, such deposition involves spin coating, in which a substrate is rapidly rotated about its axis such that centrifugal force spreads a deposited material along the substrate surface.
Many materials so deposited have a high viscosity, requiring high spin coating speeds of about 4000 rpm or higher. At such high speeds, pre-wet materials, meant to facilitate the spread of a viscous material, often spread much more quickly than the viscous material and/or evaporate, leaving the viscous material to spread along a dry surface of the substrate. An additional difficulty is the large size of modern semiconductor substrates, which increases not only the extent to which the viscous material must spread, but also the rate and degree to which pre-wet materials are lost before the viscous material has fully spread.